1. Field of the Invention
The present invention relates to a rotation transmission mechanism and a paper feeder employing the same. The rotation transmission mechanism includes a one-way clutch mounted on an outer periphery of a rotary shaft in a manner to place a clutch needle bearing in contact with the outer periphery of the rotary shaft, and a rotary member disposed on one side of the one-way clutch and engaged with the one-way clutch to be subjected to the rotation of the rotary shaft transmitted thereto. Particularly, the invention is directed to the rotation transmission mechanism wherein the clutch needle bearing of the one-way clutch is maintained in proper contact with the outer periphery of the rotary shaft even if the one-way clutch is mounted on the rotary shaft with some free play, whereby the rotary shaft is prevented from sustaining tilt-induced wear. Thus, the rotation transmission mechanism ensures that the one-way clutch provides stable transmission of the rotation of the rotary shaft to the rotary member over an extended period of time.
2. Description of the Related Art
In image forming apparatuses such as copiers, printers, facsimiles and complex machines combining these functions, cut sheets set in a paper feed cassette or on a document feed tray are fed by a pickup roller and a paper feed roller. As disclosed in Japanese Unexamined Patent Publications No. 2007-145543, No. 2010-76912, No. 2001-315986, No. 2006-76681 and the like, a rotation transmission arrangement is generally employed in which a one-way clutch is mounted on the respective rotary shafts of the pickup roller and the paper feed roller such that the rotation of the rotary shaft is transmitted to the pickup roller or the paper feed roller via the one-way clutches, thus driving the pickup roller or the paper feed roller into rotation.
In the above transmission arrangement wherein the one-way clutch is mounted on the respective rotary shafts of the pickup roller and the paper feed roller such that the rotation of the rotary shaft is transmitted to the pickup roller or to the paper feed roller via the one-way clutches, thus driving the pickup roller or the paper feed roller into rotation, a drive gear 12, 22 is fixed to a rotary shaft 11 of a paper feed roller 10 and a rotary shaft 21 of a pickup roller 20 with a pin 13, 23, respectively, as shown in FIG. 1. An intermediate gear 14 is interposed between these drive gears 12, 22 in meshing engagement therewith so that the rotary shaft 11 of the paper feed roller 10 rotates to drive the rotary shaft 21 of the pickup roller 20 into rotation in the same direction as that of the rotation of the rotary shaft 11 of the paper feed roller 10.
A one-way clutch 30 is mounted on an outer periphery of the rotary shaft 11 of the paper feed roller 10 and an outer periphery of the rotary shaft 21 of the pickup roller 20, respectively, in a manner that a clutch needle bearing 31 of the one-way clutch 30 is placed in contact with the outer periphery of each of the rotary shafts 11, 21. The one-way clutch 30 is formed with an engagement projection 32 on the opposite side thereof from the drive gear 12, 22. The engagement projection 32 is engaged with an engagement recess 15, 25 formed at each of the paper feed roller 10 and the pickup roller 20.
Thus, the rotation of the rotary shaft 11 of the paper feed roller 10 or the rotary shaft 21 of the pickup roller 20 is transmitted to the pickup roller 20 or the paper feed roller 20 via the respective one-way clutches 30 thereby driving the pickup roller 20 or the paper feed roller 10 into rotation.
A cut sheet stored in a paper feed cassette is picked up and transported as follows. As shown in FIG. 2, a backup lever 2 lifts up a leading end portion of a stack of cut sheets P stored in a paper feed cassette 1 so as to bring a cut sheet P into contact with the pickup roller 20. In this state, the paper feed roller 10 and the pickup roller 20 are rotated in the above-described manner, while the rotating pickup roller 20 picks up and feeds a top sheet of the paper stack into space between the paper feed roller 10 and a separation roller 3. The rotating paper feed roller 10, in turn, feeds the cut sheet P into space between a pair of transport rollers 4.
When the pair of transport rollers 4, with the cut sheet P so fed therebetween, starts to rotate to transport the cut sheet P, the rotary shaft 11 of the paper feed roller 10 and the rotary shaft 21 of the pickup roller 20 stop rotating.
Even if the rotary shafts 11, 21 of the paper feed roller 10 and the pickup roller 20 are in the idle state, the respective one-way clutches serve to drive the paper feed roller 10 or the pickup roller 20 to rotate together therewith.
Accordingly, the paper feed roller 10 and the pickup roller 20 rotate in conjunction with the cut sheet P transported by the transport rollers 4, so as to reduce load on the cut sheet P transported by the transport rollers 4.
In the arrangement wherein the one-way clutches 30 are mounted on the rotary shaft 11 of the paper feed roller 10 and the rotary shaft 21 of the pickup roller 20, respectively, and the engagement projections 32 formed at the one-way clutches 30 are engaged with the engagement recesses 15, 25 formed at the paper feed roller 10 and the pickup roller 20, it is a general practice to mount the one-way clutches 30 on the rotary shafts 11, 21 with some free play in consideration of assemblability and the like, as set forth in the above-described Japanese Unexamined Patent Publication No. 2001-315986.
In the case where the one-way clutches 30 are mounted on the rotary shafts 11, 21 with some free play, however, the clutch needle bearings 31 assembled in the one-way clutches 30 fail to be placed in uniform contact with the outer peripheries of the rotary shafts 11, 21. Therefore, when the paper feed roller 10 and the pickup roller 20, with the rotary shafts 11, 21 in the idle state as described above, are rotated together with the corresponding one-way clutches 30, slanted wear is produced on the rotary shafts 11, 21 of the paper feed roller 10 and the pickup roller 20 due to the non-uniform contact by the clutch needle bearings 31.
If the rotary shafts 11, 21 of the paper feed roller 10 and the pickup roller 20 suffer the slanted wear, the one-way clutches 30 may be subjected to an excessive load or the clutch needle bearings 31 of the one-way clutches 30 may fail to make proper contact with the outer peripheries of the rotary shafts 11, 21.
As a result, there occurs a problem that the one-say clutch 30 becomes unable to accomplish proper transmission of the rotation of the rotary shaft 11, 21 to the paper feed roller 10 or the pickup roller 20.